Oxygen producing apparatus



June 2, 1953 Filed Aug. 10, 1946 F. G. KEYES l OXYGEN PRODUCINGAPPARATUS l5 Sheets-Sheet l .June 2V, 1953 F. G. KEYES 2,640,332

OXYGEN PRODUCING APPARATUS Filed Aug. 10, 1946 Fig, Z

l5 Sheets-Sheet 2 Jne 2, 1953 F. G. KEYES 2,640,332

OXYGEN PRODUCING APPARATUS Filed Aug. 10, 1946 13 Shees-Sheet 5 Fig. 3

June 2, 1953 F. G. KEYES OXYGEN PRoDUcING APPARATUS Filed Aug. 1o,V 194e13 Sheets-Sheet 4 June`-2,1953 F, G, KEYES 2,640,332

OXYGEN PRODUCING APPARATUS l Filed Aug. 10, 1946 15 Sheets-Sheet 5 June2, 1953 F. G. KEYES OXYGEN PRODUCING APPARATUS 15 Sheets-Sheet 6 FiledAug. 10, 1946 June 2, 1953Y F. G. KEYES 2,640,332

OXYGEN PRODUCING APPARATUS Filed Aug. l0, 1946 15 Sheets-Sheet '7 June2, 1953 Filed Aug. l0, 1946 F. G. KEYES OXYGEN PRODUCING APPARATUS l5Sheets-Sheet 8 June 2, '1953 F. G. KEYES 2,640,332

OXYGEN PRODUCING APPARATUS Filed Aug. 10, 1946 13 Sheets-Sheet 9 NITE L/QU/ June 2, 1953 F. G. KEYES OXYGEN PRODUCING APPARATUS `Filed Aug. 10,1946 15 Sheets-Sheet lO Thi z Fig. Z1

June 2, 1953 F, G. KEYES 2,640,332

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OXYGEN PRODUCING APPARATUS Filed Aug. l0, 1946 13 Sheets-Sheet l2,f45`F1`/g.235,43 a i931 Fig. 32

, 345 Y I g 4% 46/ 406 Inv entor n 15 Sheets-Sheet 13 9.34 FL F. G.KEYES OXYGEN PRODUCING APPARATUS June 2, 1953 'Filed Aug. 1o, 194ePatented June 2, 1953 OXYGEN PRODUCING APPARATUS Frederick G. Keyes,Cambridge, Mass., assignor, by mesne assignments, to Arthur D. Little,Inc., Cambridge, Mass., a corporation of Massachusetts ApplicationAugust 10, 1946, Serial No. 689,768

16 Claims.

This invention relates to improvements in oxygen producing apparatus.More especially it has to do with the provision of a highly efficientand exceedingly compact unit for producing oxygen from atmospheric air.

In general the process follows the so-called Linde method of compressingair to a high pressure, 'cooling it at this pressure and then expandingit to a low pressure to produce liquid air. The latter is then separatedinto liquid oxygen and the remaining constituents, the most important ofwhich are nitrogen and argon. The liquid oxygen can be delivered fromthe apparatus into suitable containers but the apparatus moreparticularly provides for transforming it into high pressure oxygen gaswhich can be discharged directly into the usual portable cylinders. lfdesired both the liquid oxygen and the oxygen gas may be piped from theimproved producing apparatus to the place of immediate use.

Heretofore in the practice of the Linde methi od, the apparatus employedhas been an established plant of considerable size. It is a principalobject of this invention to provide a relatively small compact unitwhich can be placed on vehicles such as ships, trucks, aircraft andrailway cars, or which can be readily moved about industrial plants,laboratories and the like to whatever location is most convenient to theuser of the oxygen. In attaining this easily portable `unit numerousimprovements in various elements of the apparatus have been made andnovel methods have been developed.

The best mode in which the principles of the present invention have beenapplied is shown in the accompanying drawings, but these are to bedeemed merely illustrative for it is intended that lthe patent shallcover by suitable expression Vin the appended claims whatever featuresof patentable novelty exist in the improvements as a Whole.

In the accompanying drawings:

Fig. 1 is a perspective showing the oxygen producing apparatus connectedto several cylinders .for holding the high pressure gas;

Fig. 2 is an elevation Vof the apparatus alone with its cylindricalcasing and insulating material removed;

Fig. 3 is another elevation like Fig. 2, but taken from substantiallythe opposite side;

Fig. 4 is a diagrammatic representation of the Vapparatus showing thecourses of ow of the liquids and gases through the numerous elements;

Fig. 5 is an elevation of `a unit section of a preferred form of heatexchanger;

Fig. 6 is a vertical section of the same, taken as on line 6-6 of Fig.5;

Fig. 7 is a top View taken on line 'I-l of Fig. 6;

Fig. 8 is a bottom View taken as on line 8-8 of Fig. 6;

Fig. 9 is a somewhat enlarged horizontal section, taken as on line 9 9of Fig. 6, showing the multi-tube arrangement in a column of the heatexchanger;

Fig. 10 is a vertical medial section showing an automatic expansionvalve;

Fig. 11 is an enlarged horizontal section taken as on line II-ll of Fig.10;

Fig. 12 is a medial vertical section through a modied automaticexpansion valve;

Fig. 13 is a horizontal section, looking upward, taken as on line l3-I3of Fig. 12;

Fig. 14 is an enlarged horizontal section taken as on line lll-M of Fig.l2;

Fig. 15 is a medial vertical section showing a rectifier column with arotating distributor;

Fig. 16 is a horizontal section, looking upward, taken as on line lli-I6of Fig. 15;

Fig. 17 is a downwardly viewed section, taken as on line ll-ll of Fig.15;

Fig. 18 is an elevation of another form of rectifier lcolumn with partof the casing in section to show a stationary spiral distributor in fullView;

Fig. 19 is a cross section through the rectifier casing and the spiraldeilector, taken as on line |9-l9 of Fig. 18;

Fig. 20 is an enlarged View of a valve with its seat shown in medialsection;

Fig. 21 is a medial section of a vacuum jacketed exible metal hose forthe delivery of liquid oxygen;

Fig. 22 is a sectional view of the same, taken as on line 22-22 of Fig.21;

Fig. 23 is another horizontal view taken as on. line 23-23 of Fig. 21;

Fig. 24 is a vertical section, showing the exhaust tube sealed;

Fig. 25 is an elevation of the pump element;

Fig. 26 is an elevation partly in section on line 26-26 of Fig. 25;

Fig. 2.7 is a medial vertical section online 21-21 of Fig. 26 showingdetails of the driving end of the pump assembly;

Fig. 28 is a similar medial section on line 28-28 of Fig. 26 showing theoxygen end of the Dump;

Fig. 29 is a medial vertical section of the oxygen plunger;

Fig. 30 is a horizontal section taken as onv line 30--30 of Fig. 29;

Fig. 31 is a diagrammatic elevation showing the fluid connections to thevalve block of the pump;

Fig. 32 is a medial vertical section of the valve block, with some ofthe valve mechanism in full elevation;

Fig. 33 is an elevation of the valve mechanism at the beginning of thepower stroke of the pump, and a medial sectional View of certain detailsbelow the valve mechanism;

Fig. 34 is a similar view of the valve mechanism at the end of the powerstroke;

Fig. 35 is another view ofthe valve mechanisml during the exhauststroke;

Fig. 36 is a sectional View taken as on line 36-36 of Fig. 33; and

Fig. 37 is a horizontal section taken on line' 31-31 of Fig. 33.

Referring now more particularly to the drawings, and especially .toFigs. l, 2 and 3, the improved apparatus' for producing oxygen, eitheras a liquid or as a high pressure gas, or both, is extremely compact.Itis completely housed within a small cylindrical container i, on thetop cover 3 cf which are various gauges, control and connection means.The unit can be readily lifted l.lilai'lually by aid of handles E andmay be used 'wherever desired, either in a stationary location or upon avehicle. This remarkable compactness results from an eifectivearrangement of the essential elements in intimate relation and from theemployment of certain novel elements and methodsparticularly conceivedfor the purpose of saving space and producing highly efncient operation.Before considering the particular elements and the details making up theimproved apparatus, it might be well to describe the overall arrangementby reference to the diagrammatic layout of Fig. 4.y

Atmospheric air is compressed to a high pressure by any suitablecompressor A and passed through a clean-up train which may comprise anoil and liquid water separator B', one or more caustic' potash carbondioxide removers C, an aluminum oxide dehydrator D, and a glass woolfllterE. This trainis no .part of the improved unit'. and other clean-upmeans could be em- 'plo'yd instead of those suggested, provided that theair is made as completely free as possible of -liydiifcarbon, vapor fromoil of compressor, car

bon dioxide, liquid water and water vapor; This highly compressed cleanair by the light ydotted4 line' a) may all be usedi'or the production ofoxygen, butwhen' gaseous oxygen is to 'be' delivered by the apparatus'it is" a feature that a, portion of the compressed air can be utilizedtoactuate a pump to be hereinafter described. This 'use of thel air asasource or power is not essential because other means; if' desired,could be relied upon to drive the pump. This" pump driving air can beexhausted to thei atmosphere but as herein shown it is led into' theeffluent stream. Another .portion or the air supply is' employedv inconnection with the pumpto retain some'V of the refrigeration that mightotherwise be lost. This portion of the air is returned to the air streamand utilizedV in the production or the oxygen.

The air, except as above noted', is conducted through a main heatexchanger F made up of a series of unit sections f intimately arrangedand s0. connected that the flow from the bottom of one section entersthe bottom of the next adjacent sect-,ign while the flow from the topofone similarly enters the top of the next. As: the compressed i airtravels its course through a passageway of this main heat exchanger Fmuch of its heat is transferred to the cooler eiiluent and oxygen whichsimultaneously is passing through other and separated .passageways ofthe exchanger, as will presently appear.

The cooled air from the. main: exchanger F passes thence through acharcoal adsorber G and into a coil of tubing H the turns of which aresuitably spaced to allow for the free circulationv ofthe boilingoxygen-rich liquid which is not permitted to exceed a desired level inthe bottom portion"1"orso-called boiler, of a rectier column'. Theupperportion of this column is generally referred to as the distributor.During the passage of the air through this tubing H the heat'trans'ferfrom it to the surrounding bath of oxygen-rich liquid causes the air tobe transformed from the gaseous to the liquid state under the `pressureof the air feed. The liquid air (indicated by the heavy dotted line' c)'issuing from the boiler coil l-I passes through' a charcoal trap J and,preferably, a solidv carbon dioxidev filter K. It is a feature of theinvention that the liquid air is then passed through anotherV heatexchanger L, hereinafter called a liquidk air sub.- cooler, whichfurther reduces its temperature. Up to this point' in its course oftravel the air has been almost continuously giving up heat' andtherefore arrives at the dischargeend of the sub-- cooler at a very lowtemperature;

The liquid air next goes'through an expansion valve M and is immediatelyled into the top` of the rectifier colunm I, above the distributor.Whilev the expansion greatlyV reduces the pressure of the liquid aironly a small portion or it changes back to the gaseous state because of'its exceed'- ingly low temperature. For the most part the liquid airflows downward through the rectifier entering into mass' exchange withvapors having their origin in the boiler and rising upward through thecolumn. In this process the liquid airis deprived of its nitrogen andpart of the argon along with other rare gases which rise to the top ofthe column. join with whatever gaseous air may be present, and pass off'from the rectier along a course .presently to be described; Theremainingn liquid continues' downward into the bottom oi' 'the rectifierto maintain about the coil H a bath of nearly pure liquid oxygen.

This liquid' oxygen (indicated by the' heavy dash line o) maybe drainedfrom the bottom of the rectifier via a drain valve N' when desired, butordinarily the drain is closed and the flow of oxygen from the boiler isby' way of valve P under control' of a float' Q. The latter auto'-matically maintains the liquid oxygen at a predetermined level which canbe indicated b y a gauge R placed at any desired location, in thisinstance on the cover 3 of the unit container. l.

If, for any reason this valve P shouldv bev unable to pass all theliquidA loxygen produced, another line S, connected to the bottom of theboiler and thence with the line from the valve P, can be' opened bymeans of thevalve T which is normally closed.

The liquid oxygen passing the float Valve P, and such as passes throughthe line E; when open, flows through a sub-cooler 'F' comprising unitsectionsv similar to those makingV up the main heat exchanger F. Fromthe sub-cooler F the liquid oxygen goes through a wire cloth filter U,and may then be delivered from the apparatus through anoutlet V. If onlyliquid heat exchanger.

oxygen is to be produced, the described course of the oxygen would beits complete course and the high pressure pump W, about to be described,could be omitted. When gaseous oxygen, is to be a product of theapparatus, then the liquid oxygen follows a diierent course vbeyond thefilter U.

The liquid oxygen after it iiows through the sub-cooler F' and the wirecloth lter U is led to a novel pump W which transforms the relative lowpressure liquid oxygen into high pressure liquid oxygen. The highpressure oxygen (indicated by the heavy dash line o) delivered by thepump W is caused to traverse the main heat exchanger F hereinbeforementioned, through which most of the incoming compressed air is flowing.Heat is absorbed by the liquid oxygen, thus raising its temperature andcausing it to be transformed into high pressure oxygen gas (indicated bythe thin dash line 0"). When it nally leaves the heat exchanger it is atthe proper temperature and pressure to be delivered into the customarycylinders 1 (Fig. 1) for transportation to its ultimate place of use. Ifthe oxygen gas is needed as produced, as for example if the gas is to beused in a sealed cabin of a high flying airplane or within compartmentsof a submarine, it can be discharged directly from the unit through asuitable pressure reducing valve (not shown) instead of into thecustomary portable containers.

The oxygen pump as herein disclosed, and as will be more particularlydescribed later, has a cylinder and plunger at one end for highlycompressing the liquid oxygen and at its other end has another cylinderand piston to which force is applied to actuate-the oxygen plunger. Thisforce, as previously noted, may conveniently be supplied by thecompressed air, a portion of which is taken from the main line and ledas at a' to a valve block X and thence to and from the power cylinder Yof the pump. After being used there the air may be exhausted from thevalve block to atmosphere, but in the particular apparatus beingdescribed it is led into the eluent passage of the main heat exchanger.

The compressed air is also used as a thermal agent in connection withthe driving end of the pump. A tube a." leads from the branch a to theupper casing W1 of the pump and is there coiled a few turns about theoutside of the casing. 'Ihe tube then extends to the lower end of thesame upper casing W1 where it is likewise coiled a few times about thesurface of the casing. Thence the tube is connected to the air passageat some intermediate point in the main As will be more particularlydescribedlater herein, this use of the air in the coils about the uppercasing of the pump improves the thermal conditions in the power ordriving end of the pump, and saves refrigeration that otherwise would belost from the oxygen end of the pump.

Going back now to where it was noted that the eiiiuent rises in therectifier column I, it remains to point out how eifective use can bemade of this eluent for cooling purposes. The effluent (indicated by thedot-and-dash line e) is first led from the top of the rectifierv to thelower casing W2 of the pump W and serves t0 keep the temperature withinthis casing low so there will be no conversion of the liquid oxygen intogas during the intake stroke of the oxygen plunger. The compressing ofthe liquid oxygen increases its temperature and the cold eluent 6.within the casing W2 also removes this heat, a necessary item to preventvapor lock.

From the casing the eiiiuent flows next through the sub-cooler F' forthe liquid oxygen and thence passes through the sub-cooler L for theliquid air on its way from the boiler H to the expansion valve M. Lastlythe efiiuent passes to and through the main heat exchanger F, absorbingheat from the incoming compressed air, and is finally vented toatmosphere at Z.

The courses of flow of the air, oxygen and effluent are so arranged asto effect a desired and highly efhcient exchange of heat to the end thatoxygen will be produced by the apparatus as desired. Gaseous oxygen canbe delivered at substantially room temperature and at the properpressure for loading the standard storage cylinders. Also, andalternatively if desired, liquid oxygen may be collected and stored insuitable containers which currently may be purchased on the open market.

Several elements of the complete apparatus will now be described indetail.

The heat exchangers Where high pressure gases are in heat interchangerelation with lo-w pressure gases, a condition of exaggerated heattransmission imbalance is present. There -is also an inherent unbalanceof heat capacity and in certain instances, as for example where liquidoxygen is produced, there is an additional unbalance of mass or weightflow per unit of time for the diilerent fluid streams. High pressure gashas a higher heat capacity and a much larger heat transfer coelicientthan has low pressure gas. Here, in the improved apparatus for producingoxygen gas, there is the problem of heat exchange between the air at ahigh degree of compression and the elfluent at a relatively very lowpressure. In addition there is the matter of pressure drop for thefuidsowing through their respective passages. For fluids, gases in thepresent instance, assuming the same mass flow rates for the same gasdiffering only in pressure but ilowing in separate circular sectionchannels of the same cross-section, the pressure drops will be inverselyproportional to the pressures or to the densities of the gases yin theirrespective channels. The resistance to flow for a unit of mass istherefore very much less for high pressure g-as than for low pressuregas and so, unfortunately, whatever is done to increase the heattransfer also increases this resistance to flow and such increase isproportionately greater for the low pressure gas. With all the foregoingfactors in mind, the main heat exchanger disclosed herein effects .adesirable compromise of the conflicting influences and produces anenicient exchange of heat. Y

The preferred exchanger comprises one or more of what may be termed unitsections, each of which is complete in itself and may be added to orsubtracted from like sections to make the exchanger as a whole of anydesired size. For illustrative purposes, there is shown in Figs. 5 to 9inclusive, the unit section which rst receives the compressed air andfrom which the oxygen gas and eiiluent are discharged. Except iorminordetails of connections the unit section shown is representative of theothers making up the main heat exchanger F, the liquid oxygen sub-coolerF and liquid air sub-cooler L.

Each unit section f as herein shown has three columns 9, 9' and 9", eachmade up of a casing I l and a multiplicity of tubes I3 arranged in a 9.the boiler temperature is expanded via the expansion valve M, a mixtureof liquid and gaseous air results. The onlycontrol over the amount ofgas formed at the moment of expansion of the air at the top of therectifier is through con trol of the pressure in the column and the tem'perature of the liquid air entering the expansion valve. By reducing thetemperature of thelatter by utilization of the refrigeration availablein the eiuent, the proportion of ilash gas can be reduced by as much asone-half under practical operating conditions.

Automatic expansion valve This element M of the oxygen producingapparatus is an important one because a constant rectifier pressure isnecessary for the production of oxygen of consistent purity, and theexpansion valve primarily determines the rectified pressure. I f theapparatus is installed on airplanes or in submarines a form of valve isrequired which will function independently of variations in theatmospheric pressure. If the apparatus is to be always used near theground, where the atmospheric pressure may be taken as nearly constant,then another form of expansion valve will be satisfactory. Both forms ofvalve are herein disclosed.

A valve structure suitable for use where the atmospheric pressure isvariable is shown in Figs. 5

10 and 11. It comprises a pair of cylindrical casings 19 and 8| joinedby a tubular connection 83. A substantially constant pressure ismaintained in the upper casing 19 about a bellows 85 adjustably mountedtherein. 8| receives a tube through which passes the high pressureliquid air from the sub-cooler L and by means of a valve 81 the pressureof this air is reduced to that desired in the rectier. It the highpressure value changes, the valve structure as a whole respondsin suchmanner that the liquid air is nevertheless delivered to the rectifiercolumn at a substantially constant low pressure.

If the apparatus employing this type of valve is used where theatmospheric pressure. is itself constant, then the inlet 89 to thecasing 19 may be sealed or left open. But if the apparatus is used on asubmarine or an aircraft or other vehicle moving speedily from one levelto another then the inlet 89 should be sealed or connected to somesource of constant pressure. If simply sealed it is thought that thespace around the bellows 85 gradually fills with liquid air which servesreasonably well` as a constant pressure environment. One convenientsource of constant pressure could be a bulb .9| (see Fig. l5) housed ina casing 93 secured to the wall of the boiler I' of the rectier column.This bulb would contain a highly volatile fluid and be connected by atube 95 with the inlet 89 to the upper casing 19 of the expansion valve.Because the boiler temperature is normally higher than the. condensationtemperature of air and because the heat capacity inertia of the mass ofmetal and the liquid in the boiler would hinder rapid changes in thistemperature, the gas pressure in the bulb 9| and hence about the bellows85 would be maintained substantially constant.

The upper end of the bellows 85 is attached to a suitable closure plate91 which has an up'- f' standing threaded stem 99 on which is screwed aflanged nut III. (The latter may also be welded as at |93 to the closureplate 91.) The top end of the stein 99 is provided with a nearlyhemispherical. seat for aball bearing v|95 inter.-

The lower casing i posed between the closure plate stem 99 and the innerend of an adjusting stem I U1. The'latter vhas an exteriorly threadedportion I 01a to engage internal threads in a hub |09aof the end closureplate |99 for the casing 19 and has a knurled handle |8112 for turningthe stem man.- ually. The purpose of this adjustment vwill be presentlyexplained. f

The lower `end of the bellows also has ay closure plate II connected byseveral rods I3 to a guide plate I5 surrounding the flanged nut IUI andfreely movable vertically between its flange and the top closure plate91 of the bellows. 4The bottom closure plate III has adepending stem|I|a extending within and making a rather tight but nevertheless asliding iit with the tubular connector 83 which secures Vthe casings 19and 8| together. This stem I I Ia has a central bore IIIb within whichis secured the upper end of the hollow stem 81a of the valve 81. Nearthe lower end of this stern is Ia guide block |I1 for the valve stem.This block rests on a beveled shoulder 83a yon the connector and 'servesas a seat for a spring II9 which extends v between the block and thedepending stem |I|a of the lower bellows closure plate I II. Below theyblock I|1 the valve stem 81a has side openings 81b providing for theflow of pressure between the chamber |2| in the lower end of theconnector 83 and the interior of the bellows 85 via the hollow stem 81aand the lbore IIIb through the stem I I Ia and plate I I I.

At the bottom end ofthe connector 83. is 'a small central hole 83h whoseupper edge serves `as the seat for the Valve 81.l

of a tube |23 that conducts the liquid air from the subcooler L to theexpansion valve. Aroundthrough outlet |25 to the top -of the rectiercolumn I.

The cycle of regulation by the expansion valve can best be followed byassuming that the oxygen producing apparatus is started at, let us say,normal room temperature. The adjusting stem |91 will -be turned upwardby the manual handle |0112 to raise the upper closure plate 91 of thebellows. This will permit the bellows as a whole to move upward underthe'iniuence of the spring II9. Likewise the valve 81 will lift from'its seat to `an extent which will permit ready flow ofthe maximumquantity o1 `air for which the Aapparatus is designed. :Regulation ofthe low pressureA at this stage is not desired, -because cooling byi-senthalpotic expansion should be as rapid as possible.

The air when warm requires 'a' much larger opening of the valve 81, but'as the air cools the resistance to iiow diminishes and the valve may bemovedV by the handle |811) toward the' closed position to keep thepressure beyond the valve 81 reasonably constant. Turning the handlei011) advances the yadjusting stem |91, the bellows 85, and the valve B1downward, the'balancingspring |I9 being somewhat compressed during thismovement. Finally when the air is in the liquid state :and a steadytemperature is reached, the valve 81 can be ydefinitely adjustedA sothatthe pressure in the rectifier will Icorrespond-with the 'desired massflow of the air. This hand adjustment continues if the massof fluid perunit of time passing the valve 81 remains consistent` with the output ofthe air corn- Below this lhole is a hollow stem 83C in which is securedthe end not tilted but normally remains with the rectier vertical.

The top of the rectifier column illustrated in Figs. -17 is supportedfrom the cover 3 by tie rods |19. Extending through the cover 3 and asuitable packing device |80 is a shaft |8| having connection via aflexible shaft |83 with a motor |85 (see Fig. 1) mounted on the cover 3.The inner end of this shaft |8| is attached to the upper axle |81 of therotatable distributor |15, whose lower axle |89 is journaled in ananti-friction bearing |9| mounted in an upstanding hub |93 at the centerof a spider plate |95 secured to the wall |91 of the bottom portion I'of the column.

Attached to the upper axle |81 is a sort of coneshaped spider plate |99whose openings are covered by a screen 299 and whose outer depending rim|99a is secured Ito a flared section 29| of the distributor casing. Ashirt 233 upstands from this section and a cylindrical casing 235depends from it into an annular space 231 between a fixed outer shell299 and a xed inner shell 2| This space will collect enough liquid toprovide a seal for the lower end of the casing 295.

Attached to the casing 295 is another sort of cone-shaped spider plate2|3 whose apex terminates in an extended hub 2|5 at the lower end ofwhich is the lower axle |89. Between the upper outer rim 2|3a, of thisspider plate and a point midway along the hub 2|5 is a perforatedcone-shaped plate 2| 1. The formation of this perforated plate isimportant in that it must serve to permit descending liquid to drop intothe boiler I while enabling any ascending gases lto pass upward throughthe column. The perforated plate should be positioned at an angle ofapproximately from the vertical. This particular arrangement has beenfound quite satisfactory in that it provides for a rather even drippingof the liquid downward from the perforations and for a similardistributed entry of the gases moving upward into the distributor, whichis for the most part filled with surface-providing packings (not shown).

Liquid air is received through tube 22| connected to the outlet |25 (or|33) from the expansion valve. The air first enters an annular chamber223 at the very top of the column and flows downward therefrom throughseveral tubes'225 into a flash separator chamber 221. This chamber isformed in part by a casing 229 which extends upward and outward to joina sort of cover 23| which extends upward and inward 4to terminate in arolled-down neck portion 23m. The lower ends of the tubes 225 constitutenozzles 225e which are disposed so as to direct the descending liquidair beyond the neck 23m under the cover 23|. 1f any of the liquid airshould flash back to the gaseous state, the gas can liquid air fallsfrom these perforations with considerable uniformity upon thesurface-providing packings. Y I

Since the distributor as a whole 1s constantly rotating` at arelativelyslow speed, the intermingling of the liquid and the gases is markedlyuniform throughout the entire column. And because the distributor isrotating, the liquid therein is ycarried round and round whether theaxis of Vthe column is maintained vertical or is variously tiltedtherefrom.

The rising gases which reach the top of the rectifier column andconstitute the ellluent pass off through the outlet 243 and pursue thecourse hereinbefore described. The liquid drip from the distributorfalls into base I of the rectifier or what is also called the boiler.This contains the tube H coiled with many turns about a central casing245. During its flow through the coils of tube H the compressed air fromthe main heat exchanger F is transformed from the gaseous to the liquidstate. In this transformation heat is liberated from the air andabsorbed by the liquid in the boiler bathing the coiled tube.' Actuallythis latter liquid is rich in oxygen sincethe heat absorbed by it causesthe nitrogen and argon and other ingredients that might be present toboil off and pass upward through the rectifier. These vapors pick upother vapors and any gaseous air separating from the liquid air as i-tmoves downward within the distributor.

As the level of the liquid oxygen in the boiler rises, it eventuallyreaches suitably screened holes 253 in the wall of the upper casing 25|and flows therethrough into the annular space between this casing andthe upstanding hub |93 of the spider plate |95. Thence the liquid fallstherefrom through holes 255 into the central casing 245 for dischargethrough a valved outlet 251 whence it flows, as hereinbefore described,to the oxygen sub-cooler F'. The outlet 251 is controlled by a floatvalve P, to be hereinafter more particularly described, but suffice itto say the float Q and valve P normally enable all the liquid oxygenpassing through the screened holes 253 to be discharged from the outlet251 to the sub-cooler F. As previously described, if lfor any reason theproduction of liquid oxygen should exceed the flow capacity of thevalved outlet 251, a valve T can be opened and the oxygen can then passthrough the outlet 259 and through tube S to join with the flow from theoutlet 251. Thus under normal conditions the liquid level in the boileris not permitted to exceed the height determined by the screened holes253.

Figs. 18 and 19 show a rectifier column having a stationary helicaldistributor |11 therein. vThis comprises a central tube 259 (closed atboth ends) to which is `secured the inner edge of a perforated plate 26|-which is wound helically about the central tube. The outer edge of theplate is secured to the cylindrical casing 263 of the rectifier andspace between the turns of the plate is filled with suitablesurfacing-'providing packing 2|9.

Liquid air from the expansion valve enters the column through a tube22|a. It can then pass through the several chambers heretofore describedin connection with Fig. 15 and eventually drop from the severalperforated tubes 24| onto the packing 2|9. Upon the liquid encounteringthe perforated helical plate 26| it is given a sort of general clockwisemovement around the column as it descends. Some of it may, lof course,pass through the perforations 25|a of the plate. Like- `wise the gasesor vapors rising from the bottom I of the rectifier pass upward throughthe perioratons and between the packing elements and follow a generalhelical direction of flow in a counter-clockwise direction. Thus thereis an

